Electrodesalination System and Method

ABSTRACT

Systems and methods for the desalination of seawater or brackish water for the purpose of obtaining potable water. Systems may include a combination of electrodialysis and electrodeionization modules. The system configuration and process controls may achieve low energy consumption and stable operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Ser. No. 61/503,850, filed on Jul. 1,2011, titled “ELECTRODESALINATION SYSTEM AND METHOD” the entiredisclosure of which is hereby incorporated herein by reference in itsentirety for all purposes.

FIELD OF THE DISCLOSURE

Aspects relate generally to electrochemical separation and, moreparticularly, to electrochemical systems and methods for desalination.

SUMMARY

Aspects relate generally to electrodesalination systems and methods forreduced energy consumption.

In accordance with one or more aspects, a desalination system maycomprise an electrodialysis (ED) device, an electrodeionization (EDI)device fluidly connected downstream of the ED device, and a controllerconfigured to determine an optimum transition point between the ED andEDI devices with respect to power consumption and salt removal, andfurther configured to bring the EDI device online when a product streamof the ED device achieves the optimum transition point.

In accordance with one or more aspects, a method of providing potablewater may comprise fluidly connecting a seawater feed stream to an inletof an electrical purification system, the system comprising at least afirst stage and a second stage downstream of the first stage, recoveringwater from the first stage at a first rate, recovering water from thesecond stage at a second rate that is less than the first rate, andfluidly connecting an outlet of the electrical purification system to apotable point of use.

In accordance with one or more aspects, a method of providing potablewater may comprise fluidly connecting a seawater feed stream to an inletof an electrical purification system, the system comprising at least afirst electrodialysis (ED) stage and a second ED stage downstream of thefirst ED stage, inhibiting concentration polarization by passing aprocess stream through a dilute compartment in the second ED stage at anincreased velocity relative to the first ED stage, and deliveringpotable water to a point of use downstream of the electricalpurification system.

In accordance with one or more aspects, a desalination system maycomprise an electrical purification system comprising at least a firstelectrodialysis (ED) stage and a second ED stage fluidly connecteddownstream of the first ED stage, at least one conductivity sensorassociated with the electrical purification system, and a controllerconfigured to apply a first voltage to the first ED stage and to apply asecond voltage, lower than the first voltage, to the second ED stagebased on input from the conductivity sensor to inhibit concentrationpolarization.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Embodimentsdisclosed herein may be combined with other embodiments in any mannerconsistent with at least one of the principles disclosed herein, andreferences to “an embodiment,” “some embodiments,” “an alternateembodiment,” “various embodiments,” “one embodiment” or the like are notnecessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described may beincluded in at least one embodiment. The appearances of such termsherein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. Where technicalfeatures in the figures, detailed description or any claim are followedby references signs, the reference signs have been included for the solepurpose of increasing the intelligibility of the figures anddescription. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every figure. In the figures:

FIGS. 1-2 present PID control schematics in accordance with one or moreembodiments;

FIGS. 3-4 present data discussed in accompanying Example 3 in accordancewith one or more embodiments;

FIG. 5 presents a process diagram discussed in accompanying Example 2 inaccordance with one or more embodiments;

FIGS. 6A-6D present data discussed in accompanying Example 2 inaccordance with one or more embodiments;

FIG. 7 presents a schematic of system configurations discussed inaccompanying Example 4 in accordance with one or more embodiments;

FIGS. 8-10 present data discussed in accompanying Example 4 inaccordance with one or more embodiments;

FIG. 11 presents a schematic of a spacer configuration discussed inaccompanying Example 5 in accordance with one or more embodiments;

FIG. 12 presents an example of equilibrium data and related conductivityin accordance with one or more embodiments;

FIGS. 13-14 present data discussed in accompanying Example 6 inaccordance with one or more embodiments;

FIG. 15 presents a system schematic as discussed in accompanying Example7 in accordance with one or more embodiments.

DETAILED DESCRIPTION

Devices for purifying fluids with electrical fields are commonly used totreat water and other liquids containing dissolved ionic species. Twotypes of devices that treat water in this way are electrodeionizationand electrodialysis devices. Within these devices are concentrating anddiluting compartments separated by ion-selective membranes. Anelectrodialysis device typically includes alternating electroactivesemipermeable anion and cation exchange membranes. Spaces between themembranes are configured to create liquid flow compartments with inletsand outlets. An applied electric field imposed via electrodes causesdissolved ions, attracted to their respective counter-electrodes, tomigrate through the anion and cation exchange membranes. This generallyresults in the liquid of the diluting compartment being depleted ofions, and the liquid in the concentrating compartment being enrichedwith the transferred ions.

Electrodeionization (EDI) is a process that removes, or at leastreduces, one or more ionizcd or ionizable species from water usingelectrically active media and an electric potential to influence iontransport. The electrically active media typically serves to alternatelycollect and discharge ionic and/or ionizable species and, in some cases,to facilitate the transport of ions, which may be continuously, by ionicor electronic substitution mechanisms. EDI devices can compriseelectrochemically active media of permanent or temporary charge, and maybe operated batch-wise, intermittently, continuously, and/or even inreversing polarity modes. EDI devices may be operated to promote one ormore electrochemical reactions specifically designed to achieve orenhance performance. Further, such electrochemical devices may compriseelectrically active membranes, such as semi-permeable or selectivelypermeable ion exchange or bipolar membranes. Continuouselectrodeionization (CEDI) devices are EDI devices known to thoseskilled in the art that operate in a manner in which water purificationcan proceed continuously, while ion exchange material is continuouslyrecharged. CEDI techniques can include processes such as continuousdeionization, filled cell electrodialysis, or electrodiaresis. Undercontrolled voltage and salinity conditions, in CEDI systems, watermolecules can be split to generate hydrogen or hydronium ions or speciesand hydroxide or hydroxyl ions or species that can regenerate ionexchange media in the device and thus facilitate the release of thetrapped species therefrom. In this manner, a water stream to be treatedcan be continuously purified without requiring chemical recharging ofion exchange resin.

Electrodialysis (ED) devices operate on a similar principle as CEDI,except that ED devices typically do not contain electroactive mediabetween the membranes. Because of the lack of electroactive media, theoperation of ED may be hindered on feed waters of low salinity becauseof elevated electrical resistance. Also, because the operation of ED onhigh salinity feed waters can result in elevated electrical currentconsumption, ED apparatus have heretofore been most effectively used onsource waters of intermediate salinity. In ED based systems, becausethere is no electroactive media, splitting water is inefficient andoperating in such a regime is generally avoided.

In CEDI and ED devices, a plurality of adjacent cells or compartmentsare typically separated by selectively permeable membranes that allowthe passage of either positively or negatively charged species, buttypically not both. Dilution or depletion compartments are typicallyinterspaced with concentrating or concentration compartments in suchdevices. As water flows through the depletion compartments, ionic andother charged species are typically drawn into concentratingcompartments under the influence of an electric field, such as a DCfield. Positively charged species are drawn toward a cathode, typicallylocated at one end of a stack of multiple depletion and concentrationcompartments, and negatively charged species are likewise drawn towardan anode of such devices, typically located at the opposite end of thestack of compartments. The electrodes are typically housed inelectrolyte compartments that are usually partially isolated from fluidcommunication with the depletion and/or concentration compartments. Oncein a concentration compartment, charged species are typically trapped bya barrier of selectively permeable membrane at least partially definingthe concentration compartment. For example, anions are typicallyprevented from migrating further toward the cathode, out of theconcentration compartment, by a cation selective membrane. Once capturedin the concentrating compartment, trapped charged species can be removedin a concentrate stream.

In both CEDI and ED devices, the DC field is typically applied to thecells from a source of voltage and electric current applied to theelectrodes (anode or positive electrode, and cathode is or negativeelectrode). The voltage and current source (collectively “power supply”)can be itself powered by a variety of means such as an AC power source,or for example, a power source derived from solar, wind, or wave power.At the electrode/liquid interfaces, electrochemical half cell reactionsoccur that initiate and/or facilitate the transfer of ions through themembranes and compartments. The specific electrochemical reactions thatoccur at the electrode/interfaces can be controlled to some extent bythe concentration of salts in the specialized compartments that housethe electrode assemblies. For example, a feed to the anode electrolytecompartments that is high in sodium chloride will tend to generatechlorine gas and hydrogen ion, while such a feed to the cathodeelectrolyte compartment will tend to generate hydrogen gas and hydroxideion. Generally, the hydrogen ion generated at the anode compartment willassociate with a free anion, such as chloride ion, to preserve chargeneutrality and create hydrochloric acid solution, and analogously, thehydroxide ion generated at the cathode compartment will associate with afree cation, such as sodium, to preserve charge neutrality and createsodium hydroxide solution. The reaction products of the electrodecompartments, such as generated chlorine gas and sodium hydroxide, canbe utilized in the process as needed for disinfection purposes, formembrane cleaning and defouling purposes, and for pH adjustmentpurposes.

Plate-and-frame and spiral wound designs have been used for varioustypes of electrochemical dcionization devices including but not limitedto ED and EDI devices. Commercially available ED devices are typicallyof plate-and-frame design, while EDI devices are available in both plateand frame and spiral configurations. Various embodiments are applicableto plate-and frame, spiral wound, and cross-flow designs as discussedherein.

One or more embodiments relate to devices that may purify fluidselectrically that may be contained within a housing, as well as methodsof manufacture and use thereof. Liquids or other fluids to be purifiedenter the purification device or apparatus and, under the influence ofan electric field, are treated to produce an ion-depleted liquid.Species from the entering liquids are collected to produce anion-concentrated liquid. The components of the electrical purificationapparatus, which may also be referred to as an electrochemicalseparation system or an electrochemical separation device, may beassembled using various techniques to achieve optimal operation of theapparatus.

The power consumption of sea water desalination processes has been along standing barrier to wide spread acceptance of using desalinationfor the production of potable water. The typical power consumption canrange from about 3.5 kwh/m³ for a pressure driven process such asreverse osmosis to more than 10 kwh/m³ for a thermal desalinationprocess.

The use of electrically driven electrochemical deionization processessuch as electrodialysis and electrodeionization has traditionally beenlimited to purifying water with less ionic content than sea water.However, a power consumption of about 1.8 kwh/m³ may be achieved whenusing a combination of electrochemical separation devices in accordancewith one or more embodiments. In accordance with certain embodiments,potable water may be produced from seawater at an energy value of about1.5 kWh/m³ or less.

As used herein, “purify” relates to reducing the total dissolved solidscontent and optionally to reducing the concentration of suspendedsolids, colloidal content and ionized and non-ionized impurities in asource water to a level where the purified water has been renderedpotable and can be used for fresh water purposes such as, but notlimited to, human and animal consumption, irrigation, and industrialapplications. Desalination is a type of purification in which salt isremoved from seawater. One or more embodiments may pertain todesalination of seawater. The feed water or water to be treated may befrom a variety of sources including those having a TDS content ofbetween about 3,000 ppm and about 40,000 ppm, or more. Feed water canbe, for example, seawater from the ocean, brackish water, gray water,industrial effluent, and oil fill recovery water. The feed water maycontain high levels of monovalent salts, divalent and multivalent salts,and organic species. In some embodiments, notable aspects may involvemethods of treating or desalinating a process water or a feed waterconsisting of or consisting essentially of seawater. The water may beprocessed to a desired or required level of purity.

In accordance with one or more embodiments, the process stream maygenerally comprise a water stream deliverable to the electrochemicaldevice for treatment. In some embodiments, the process stream maygenerally comprise a salt solution. A salt solution may contain a singlesalt species or a mixture of salt species, for example, as may bepresent in seawater. In at least one embodiment, the process stream maycomprise non-potable water. Potable water typically has a totaldissolved solids (TDS) content of less than about 1,500 ppm. In someembodiments, potable water may have a TDS of less than about 1,000 ppm.In some cases, potable water may have a TDS content of less than about500 ppm. In some non-limiting embodiments, potable water may have a TDScontent of less than about 250 ppm. Examples of non-potable water mayinclude seawater or salt water, brackish water, gray water, and someindustrial water. A process stream may include target species such aschloride, sulfate, bromide, silicate, iodide, phosphate, sodium,magnesium, calcium, potassium, nitrate, arsenic, lithium, boron,strontium, molybdenum, manganese, aluminum, cadmium, chromium, cobalt,copper, iron, lead, nickel, selenium, silver and zinc. In accordancewith one or more embodiments, the invention is directed to a method oftreating seawater or brackish water where the source water comprises asolute mixture. In some embodiments, monovalent ions may be at a higherconcentration as compared to the concentrations of divalent and othermultivalent ions. References to seawater herein are generally applicableto other forms of non-potable water.

In some embodiments of the disclosure, a method of providing a source ofpotable water is provided. In certain embodiments, a method offacilitating the production of potable water from seawater is provided.The method may comprise providing an electrical purification apparatuscomprising a cell stack. The method may further comprise fluidlyconnecting a seawater feed stream to an inlet of the electricalpurification apparatus. The method may further comprise fluidlyconnecting an outlet of the electrical purification apparatus to apotable point of use. Seawater or estuary water may have a concentrationof total dissolved solids in a range of about 10,000 to about 45,000ppm. In certain examples, the seawater or estuary water may have aconcentration of total dissolved solids of about 35,000 ppm.

Other types of feed water comprising different concentrations of totaldissolved solids may be treated or processed using the apparatus andmethods of the present disclosure. For example, brackish water, having atotal dissolved solids content in a range of about 1000 ppm to about10,000 ppm may be treated to produce potable water. Brine, having atotal dissolved solids content in a range of about 50,000 ppm to about150,000 ppm may be treated to produce potable water. In someembodiments, brine, having a total dissolved solids content in a rangeof about 50,000 ppm to about 150,000 ppm may be treated to produce awater having a lower total dissolved solids content for purposes ofdisposal, for example, to a body of water, such as an ocean.

In accordance with one or more embodiments, an electrodialysis moduleincludes cation exchange and anion exchange membranes separated by aspacer comprising a screen and gasket, for example. Numerous repeatingpairs of this combination are used to make an electrodialysis module. Insome non-limiting embodiments, there may be about 100 to 1000 repeatingpairs or cell pairs in a module. Each cell pair may include a dilutecompartment and a concentrate compartment. As water is passed throughthe cell pairs, an electric field generated by a direct current (DC)power supply may be imposed perpendicular to the water flow. This mayresult in the migration of ions from the dilute compartment to theconcentrate compartment through the ion exchange membranes. Indesalination operations, salt ions may be transferred through ionexchange membranes. Cations will transfer through the cation membraneand anions will transfer through the anion membrane. Water from the cellpairs may be combined in manifolds within the electrodialysis module.Two water streams may exit the module, a dilute stream and a concentratestream. Electrodeionization may also use cation exchange and anionexchange membranes separated by a spacer with a void volume filled withan ion exchange material such as ion exchange beads, felts and the like.In some embodiments, an electrodeionization device may include an ionexchange screen. In accordance with one or more embodiments, an ionexchange screen may be a functionalized screen, such as a screen havingcation and/or anion functionality. The use of ion exchange material inplace of an inert screen may improve the ability of theelectrodeionization device to remove ions from water when the water isdilute, for example, less than about 5000 mg/l of ionic concentration.The ion exchange material can comprise either cation exchange or anionexchange material and combinations thereof.

In accordance with one or more embodiments, an electrochemicalseparation system or device may be modular. Each modular unit maygenerally function as a sub-block of an overall electrochemicalseparation system. A modular unit may include any desired number of cellpairs. In some embodiments, the number of cell pairs per modular unitmay depend on the total number of cell pairs and passes in theseparation device. It may also depend on the number of cell pairs thatcan be thermally bonded and potted in a frame with an acceptable failurerate when tested for cross-leaks and other performance criteria. Thenumber can be based on statistical analysis of the manufacturing processand can be increased as process controls improve. In some non-limitingembodiments, a modular unit may include about 50 cell pairs. Modularunits may be individually assembled and quality control tested, such asfor leakage, separation performance and pressure drop prior to beingincorporated into a larger system. In some embodiments, a cell stack maybe mounted in a frame as a modular unit that can be testedindependently. A plurality of modular units can then be assembledtogether to provide an overall intended number of cell pairs in anelectrochemical separation device. In some embodiments, an assemblymethod may generally involve placing a first modular unit on a secondmodular unit, placing a third modular unit on the first and secondmodular units, and repeating to obtain a plurality of modular units of adesired number. In some embodiments, the assembly or individual modularunits may be inserted into a pressure vessel for operation. Multi-passflow configurations may be possible with the placement of blockingmembranes and/or spacers between modular units or within modular units.A modular approach may improve manufacturability in terms of time andcost savings. Modularity may also facilitate system maintenance byallowing for the diagnosis, isolation, removal and replacement ofindividual modular units. Individual modular units may includemanifolding and flow distribution systems to facilitate anelectrochemical separation process. Individual modular units may be influid communication with one another, as well as with centralmanifolding and other systems associated with an overall electrochemicalseparation process.

In accordance with one or more embodiments, the efficiency ofelectrochemical separation systems may be improved. Current loss is onepotential source of inefficiency. In some embodiments, such as thoseinvolving a cross-flow design, the potential for current leakage may beaddressed. Current efficiency may be defined as the percentage ofcurrent that is effective in moving ions out of the dilute stream intothe concentrate stream. Various sources of current inefficiency mayexist in an electrochemical separation system. One potential source ofinefficiency may involve current that bypasses the cell pairs by flowingthrough the dilute and concentrate inlet and outlet manifolds. Openinlet and outlet manifolds may be in direct fluid communication withflow compartments and may reduce pressure drop in each flow path. Partof the electrical current from one electrode to the other may bypass thestack of cell pairs by flowing through the open areas. The bypasscurrent reduces current efficiency and increases energy consumption.Another potential source of inefficiency may involve ions that enter thedilute stream from the concentrate due to imperfect permselectivity ofion exchange membranes. In some embodiments, techniques associated withthe sealing and potting of membranes and screens within a device mayfacilitate reduction of current leakage.

In one or more embodiments, a bypass path through a stack may bemanipulated to promote current flow along a direct path through a cellstack so as to improve current efficiency. In some embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths are more tortuous than a direct paththrough the cell stack. In at least certain embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths present higher resistance than a directpath through the cell stack. In some embodiments involving a modularsystem, individual modular units may be configured to promote currentefficiency. Modular units may be constructed and arranged to provide acurrent bypass path that will contribute to current efficiency. Innon-limiting embodiments, a modular unit may include a manifold systemand/or a flow distribution system configured to promote currentefficiency. In at least some embodiments, a frame surrounding a cellstack in an electrochemical separation modular unit may be constructedand arranged to provide a predetermined current bypass path. In someembodiments, promoting a multi-pass flow configuration within anelectrochemical separation device may facilitate reduction of currentleakage. In at least some non-limiting embodiments, blocking membranesor spacers may be inserted between modular units to direct dilute and/orconcentrate streams into multiple-pass flow configurations for improvedcurrent efficiency. In some embodiments, current efficiency of at leastabout 60% may be achieved. In other embodiments, a current efficiency ofat least about 70% may be achieved. In still other embodiments, acurrent efficiency of at least about 80% may be achieved. In at leastsome embodiments, a current efficiency of at least about 85% may beachieved.

In accordance with one or more embodiments, a method for preparing acell stack for an electrical purification apparatus may comprise formingcompartments. A first compartment may be formed by securing ion exchangemembranes to one another to provide a first spacer assembly having afirst spacer disposed between the ion exchange membranes. For example, afirst cation exchange membrane may be secured to a first anion exchangemembrane at a first portion of a periphery of the first cation exchangemembrane and the first anion exchange membrane to provide a first spacerassembly having a first spacer disposed between the first cationexchange membrane and the first anion exchange membrane.

A second compartment may be formed by securing ion exchange membranes toone another to provide a second spacer assembly having a second spacerdisposed between the ion exchange membranes. For example, a second anionexchange membrane may be secured to a second cation exchange membrane ata first portion of a periphery of the second cation exchange membraneand the second anion exchange membrane to provide a second spacerassembly having a second spacer disposed between the second anionexchange membrane and the second cation exchange membrane.

A third compartment may be formed between the first compartment and thesecond compartment by securing the first spacer assembly to the secondspacer assembly, and by positioning a spacer therebetween. For example,the first spacer assembly may be secured to the second spacer assemblyat a second portion of the periphery of the first cation exchangemembrane and at a portion of the periphery of the second anion exchangemembrane to provide a stack assembly having a spacer disposed betweenthe first spacer assembly and the second spacer assembly.

In some non-limiting embodiments, each of the first compartment and thesecond compartment may be constructed and arranged to provide adirection of fluid flow that is different from the direction of fluidflow in the third compartment. For example, the fluid flow in the thirdcompartment may be running in a direction of a 0° axis. The fluid flowin the first compartment may be running at 30°, and the fluid flow inthe second compartment may be running at the same angle as the firstcompartment (30°) or at another angle, such as 120°. The method mayfurther comprise securing the assembled cell stack within a housing.

In accordance with one or more embodiments, an electrochemicalseparation system may include a cross-flow design. A cross-flow designmay allow for increased membrane utilization, lower pressure drop and areduction in external leaks. Additionally, limitations on operatingpressure may be reduced by a cross-flow design. In at least someembodiments, the pressure rating of a shell and endcaps may be the onlysubstantial limitations on operating pressure. Automation ofmanufacturing processes may also be achieved.

In accordance with one or more embodiments, a first fluid flow path anda second fluid flow path may be selected and provided by way of theportions of the peripheries of the ion exchange membranes that aresecured to one another. Using the first fluid flow path as a directionrunning along a 0° axis, the second fluid flow path may run in adirection of any angle greater than zero degrees and less than 360°. Incertain embodiments of the disclosure, the second fluid flow path mayrun at a 90° angle, or perpendicular to the first fluid flow path. Inother embodiments, the second fluid flow path may run at a 180° angle tothe first fluid flow path. If additional ion exchange membranes aresecured to the cell stack to provide additional compartments, the fluidflow paths in these additional compartments may be the same or differentfrom the first fluid flow path and the second fluid flow path. Incertain embodiments, the fluid flow path in each of the compartmentsalternates between a first fluid flow path and a second fluid flow path.For example, the first fluid flow path in the first compartment may berunning in a direction of 0°. The second fluid flow path in the secondcompartment may be running in a direction of 90°, and the third fluidflow path in the third compartment may be running in a direction of 0°.In certain examples, this may be referred to as cross-flow electricalpurification.

In other embodiments, the fluid flow path in each of the compartmentsalternates sequentially between a first fluid flow path, a second fluidflow path, and a third fluid flow path. For example, the first fluidflow path in the first compartment may be running in a direction of 0°.The second fluid flow path in the second compartment may be running at30°, and the third fluid flow path in the third compartment may berunning at 90°. The fourth fluid flow path in the fourth compartment maybe running at 0°. In another embodiment, the first fluid flow path inthe first compartment may be running in a direction of 0°. The secondfluid flow path in the second compartment may be running at 60°, and thethird fluid flow path in the third compartment may be running at 120°.The fourth fluid flow path in the fourth compartment may be running at0°. In some embodiments, one or more flow paths may be substantiallynon-radial. In at least some embodiments, one or more flow paths mayfacilitate achieving a substantially uniform liquid flow velocityprofile within the system.

In accordance with one or more embodiments, the flow within acompartment may be adjusted, redistributed, or redirected to providegreater contact of the fluid with the membrane surfaces within thecompartment. The compartment may be constructed and arranged toredistribute fluid flow within the compartment. The compartment may haveobstructions, projections, protrusions, flanges, or baffles that mayprovide a structure to redistribute the flow through the compartment,which will be discussed further below. In certain embodiments, theobstructions, projections, protrusions flanges, or baffles may bereferred to as a flow redistributor. A flow redistributor may be presentin one or more of the compartments of the cell stack.

In some embodiments, the plurality of ion exchange membranes secured toone another may alternate between cation exchange membranes and anionexchange membranes to provide a series of ion diluting compartments andion concentrating compartments.

The geometry of the membranes may be of any suitable geometry such thatthe membranes may be secured within a cell stack. In certainembodiments, a particular number of corners or vertices on the cellstack may be desired so as to suitably secure the cell stack within ahousing. In certain embodiments, particular membranes may have differentgeometries than other membranes in the cell stack. The geometries of themembranes may be selected to assist in at least one of securing themembranes to one another, to secure spacers within the cell stack, tosecure membranes within a modular unit, to secure membranes within asupport structure, to secure a group of membranes such as a cell stackto a housing, and to secure a modular unit into a housing.

In some embodiments of the disclosure, an electrical purificationapparatus comprising a cell stack is provided. The electricalpurification apparatus may comprise a first compartment comprising ionexchange membranes and may be constructed and arranged to provide adirect fluid flow in a first direction between the ion exchangemembranes. The electrical purification apparatus may also comprise asecond compartment comprising ion exchange membranes and may beconstructed and arranged to provide a direct fluid flow in a seconddirection. Each of the first compartment and the second compartment maybe constructed and arranged to provide a predetermined percentage ofsurface area or membrane utilization for fluid contact. In certainembodiments, the membrane utilization that may be achieved is greaterthan 65%. In other embodiments, the membrane utilization that may beachieved is greater than 75%. In certain other embodiments, the membraneutilization that may be achieved may be greater than 85%. The membraneutilization may be at least in part dependent on the methods used tosecure each of the membranes to one another, and the design of thespacer. In order to obtain a predetermined membrane utilization,appropriate securing techniques and components may be selected in orderto achieve a reliable and secure seal that allows optimal operation ofthe electrical purification apparatus, without encountering leakagewithin the apparatus, while maintaining a large surface area of membranethat may be used in the process.

For example an electrical purification apparatus comprising a cell stackmay be provided. The electrical purification apparatus may comprise afirst compartment comprising a first cation exchange membrane and afirst anion exchange membrane, the first compartment constructed andarranged to provide a direct fluid flow in a first direction between thefirst cation exchange membrane and the first anion exchange membrane.The apparatus may also comprise a second compartment comprising thefirst anion exchange membrane and a second cation exchange membrane toprovide a direct fluid flow in a second direction between the firstanion exchange membrane and the second cation exchange membrane. Each ofthe first compartment and the second compartment may be constructed andarranged to provide a predetermined membrane utilization, for example, afluid contact of greater than 85% of the surface area of the firstcation exchange membrane, the first anion exchange membrane and thesecond cation exchange membrane. At least one of the first compartmentand the second compartment may comprise a spacer, which may be ablocking spacer. The direct fluid flow in the first direction and thesecond direction may be selected and provided by the construction andarrangement of the compartments.

The electrical purification apparatus comprising a cell stack mayfurther comprise a housing enclosing the cell stack, with at least aportion of a periphery of the cell stack secured to the housing. A framemay be positioned between the housing and the cell stack to providefirst modular unit in the housing. A flow redistributor may be presentin one or more of the compartments of the cell stack. At least one ofthe compartments may be constructed and arranged to provide flowreversal within the compartment.

In some embodiments of the disclosure, a cell stack for an electricalpurification apparatus is provided. The cell stack may provide aplurality of alternating ion depleting and ion concentratingcompartments. Each of the ion depleting compartments may have an inletand an outlet that provides a dilute fluid flow in a first direction.Each of the ion concentrating compartments may have an inlet and anoutlet that provides a concentrated fluid flow in a second directionthat is different from the first direction. A spacer may be positionedin the cell stack. The spacer may provide structure to and define thecompartments and, in certain examples, may assist in directing fluidflow through the compartment. The spacer may be a blocking spacer whichmay be constructed and arrange to redirect at least one of fluid flowand electrical current through the cell stack. As discussed, theblocking spacer may reduce or prevent electrical current inefficienciesin the electrical purification apparatus.

In some embodiments of the disclosure, an electrical purificationapparatus is provided. The apparatus may comprise a cell stackcomprising alternating ion diluting compartments and ion concentratingcompartments. Each of the ion diluting compartments may be constructedand arranged to provide a fluid flow in a first direction. Each of theion concentrating compartments may be constructed and arranged toprovide a fluid flow in a second direction that is different from thefirst direction. The electrical purification apparatus may also comprisea first electrode adjacent an first ion exchange membrane at a first endof the cell stack, and a second electrode adjacent a second ion exchangemembrane at a second end of the cell stack. Each of the first ionexchange membrane and the second ion exchange membrane may be an anionexchange membrane or a cation exchange membrane. For example, the firstion exchange membrane may be an anion exchange membrane, and the secondion exchange membrane may be a cation exchange membrane. The apparatusmay further comprise a blocking spacer positioned in the cell stack andconstructed and arranged to redirect at least one of a dilute fluid flowand a concentrate fluid flow through the electrical purificationapparatus and to prevent a direct current path between the firstelectrode and the second electrode. As discussed above, the blockingspacer may be constructed and arranged to reduce electrical currentinefficiencies in the electrical purification apparatus.

The cell stack for the electrical purification apparatus may be enclosedin a housing with at least a portion of a periphery of the cell stacksecured to the housing. A frame may be positioned between the housingand the cell stack to provide first modular unit in the housing. Asecond modular unit may also be secured within the housing. A blockingspacer may also be positioned between the first modular unit and thesecond modular unit. A flow redistributor may be present in one or moreof the compartments of the cell stack. At least one of the compartmentsmay be constructed and arranged to provide flow reversal within thecompartment. A bracket assembly may be positioned between the frame andthe housing to provide support to the modular unit and to secure themodular unit within the housing. In certain embodiments of thedisclosure, an electrical purification apparatus is provided thatreduces or prevents inefficiencies resulting from greater electricalpower consumption. The electrical purification apparatus of the presentdisclosure may provide for a multiple pass flow configuration to reduceor prevent current inefficiencies. The multiple pass flow configurationmay reduce the bypass of current through the flow manifolds, or leakageof current, by eliminating or reducing the direct current path betweenthe anode and the cathode of the electrical purification apparatus.

In certain embodiments of the disclosure the flow within a compartmentmay be adjusted, redistributed, or redirected to provide greater contactof the fluid with the membrane surfaces within the compartment. Thecompartment may be constructed and arranged to redistribute fluid flowwithin the compartment. The compartment may have obstructions,projections, protrusions, flanges, or baffles that may provide astructure to redistribute the flow through the compartment. Theobstructions, projections, protrusions, flanges, or baffles may beformed as part of ion exchange membranes, the spacer, or may be anadditional separate structure that is provided within the compartment.The obstructions, projections, protrusions, flanges, or baffles may beformed by providing an extension from an adhesive that may secure theion exchange membranes to one another. The spacer may be impregnatedwith thermoplastic rubber to form protrusions that may be bonded withadhesive to adjacent membranes. The thermoplastic rubber may be appliedto the spacer using processes such as thermo-compression or rotaryscreen printing. The compartments may or may not contain ion exchangeresin.

In accordance with one or more embodiments, water is purified under thepresence of an electric field via electrodialysis. Water in the dilutecompartment becomes purer while the water in the adjacent concentratecompartment becomes enriched with ionic compounds. This may result inthe electrical resistance of the module increasing since the dilutewater is not very conductive. Furthermore, if the water in the dilutecompartment becomes too pure, water will dissociate near the ionexchange membrane leading to a layer of very high electrical resistancewater directly adjacent to the ion exchange membrane that increases theoverall applied voltage. This inefficiency can limit the electrodialysisprocess to conditions where these phenomena will not occur. In order tominimize this effect also referred to as concentration polarization,various process modifications can be performed in accordance with one ormore embodiments.

In some embodiments, fluid velocity within the dilute compartment may beadjusted to avoid concentration polarization. By increasing the flowvelocity through each spacer, the boundary layer may be decreased nearthe membrane which may improve the mixing of water within the spacer andmay therefore lessen the effects of concentration polarization. Forexample, an electrodialysis process may be performed with a lowervelocity when the water has sufficient conductivity to avoidconcentration polarization and a higher velocity as the water becomesmore dilute. For instance, in a multi-stage process that includesseveral electrodialysis stages in series, the fluid velocity in laterstages may be increased when the water is purer by using fewer numbersof cell pairs.

In addition, an electrodialysis module may be modified so that there aremultiple passes through the electric field contained within a singlemodule. In accordance with one or more embodiments, velocity can beincreased in the same ED module by reducing the number of cell pairs perpass in the ED module. Multiple passes within one module may be referredto as a folded path module. As a non-limiting example, for a five passfolded path module in a single electrodialysis module, the number ofcell pairs in each pass may be modified to include 182 cell pairs forthe first pass, 164 cell pairs for the second pass, 148 cell pairs forthe third pass, 130 cell pairs for the fourth pass and 120 cell pairsfor the fifth and final pass. By changing the velocity, the boundarylayer next to the ion exchange membranes may be modified resulting inlower concentration polarization effects which also reduces theelectrical resistance of the module. Embodiments are not limited to thenumber of stages, the number of passes within a stage, the number ofcell pairs in each stage or the flow path length of either theelectrodialysis or electrodeionization module.

In accordance with one or more embodiments, velocity may be increasedwith decreasing concentration polarization or pass. Concentrationpolarization and limiting current density in an ED operation isgenerally governed by solution concentration, current density andvelocity of diluting compartment. To prevent limiting current in EDoperations for seawater, velocity of the dilute compartment may beincreased in the later stages of the desalting process in accordancewith one or more embodiments. Avoiding desalting at limiting currentdensity may result in lower module resistance, (i.e. lower energyconsumption), lower risk of scaling (i.e. reduced generation of OHions), and improved current efficiency (i.e. reduced module resistanceand reduced risk of electrical shorting or leakage).

In accordance with one or more embodiments, the power consumption andthe concentration polarization of the electrodesalination systemcomprising electrodialysis and electrodeionization modules may bereduced by applying different voltages to each stage of a multistagesystem. Water from the first stage may be transferred to the secondstage and then to the third stage and beyond. A higher voltage and/orgreater current density can be used in stages where the amount of ioniccontent in the water to be desalinated is greater and then decreased asthe water becomes more pure such that later stages have a lower currentdensity. In one non-limiting example, the current density on the firststage being fed with seawater may be about 23.1 A/m², the second stagemay be about 17.8 A/m² and the third stage may be about 5.5 A/m². Insome embodiments, the inlet and outlet conductivity may be measured witha conductivity sensor for each electrodialysis stage. Select voltagesmay then be applied so that concentration polarization does not occur.In another embodiment, a proportional-integral-derivative (PID) controlas shown in FIG. 1 may be used to control the operation of each stage ina multi-stage electrodialysis/electrodeionization desalination process.The PID controller may use feedback, for instance the inlet and outletconductivity from each stage, and calculate an error from a set point ofthe desired output of the stage compared to the actual reading. FIG. 2illustrates a PID controller in accordance with one or more embodiments.Table 1 presents a non-limiting example of a control simulation.

TABLE 1 Feed Water Stage 1 Current Stage 1 Stage 2 Current Stage 2 Stage3 Current Stage 3 Stage 4 Current Stage 4 Quality Removal RequiredProduct Removal Required Product Removal Required Product RemovalRequired Product (ppm) (%) (A) (ppm) (%) (A) (ppm) (%) (A) (ppm) (%) (A)(ppm) 35000 50 4.6 17600 50 2.3 0750 50 1.1 4375 44 1.0 500 25000 50 3.312500 50 1.6 0260 50 0.6 2125 42 0.7 500 10000 50 1.3 8000 60 0.7 250050 0.3 1260 30 0.2 500

In accordance with one or more embodiments, the PID controller mayadjust the applied voltage to minimize the error between the set pointand actual output conductivity from each stage. The flow rate may alsobe adjusted. The PID control may compensate for changes in the inletconductivity which helps minimize concentration polarization. In someembodiments, a PID control may be set with gain parameters for theproportional, integral and derivate functions along with a conductivityset point for each stage, for instance 25 mS/cm for Stage 1. Duringoperation, seawater may be fed to the first stage and the PID controllermay adjust the applied voltage of the first stage so that an outletconductivity near the set point is obtained. This may maximizeefficiency in each stage which may help to minimize the overall powerconsumption of the desalination process while reducing the concentrationpolarization. In a further embodiment, a pH sensor may be used on theinlet and outlet of the electrodeionization or electrodialysis moduleeither on the dilute and/or concentrate stream to detect a pH shift dueto water splitting or water dissociation caused by concentrationpolarization. The applied voltage or flow rate can be adjusted tocontrol the pH and thus minimize concentration polarization. A PIDcontroller can be used to control the pH. This may help to maximize theefficiency and minimize the power consumption of the electrodesalinationsystem.

In another embodiment, the water recovery may be adjusted on each stageto impact the power consumption. The salt concentration across an ionexchange membrane may generate a Donnan voltage. This voltage, alsoreferred to as the thermodynamic voltage, can be thought of as theminimum voltage needed to electrically drive ions from the dilutecompartment to the concentrate compartment. The Nernst equation may beused to calculate the Donnan voltage.

In accordance with one or more embodiments, variable water recovery maybe applied to different ED stages. During desalination process, thelater desalting stage can be operated at lower water recovery tominimize the concentration difference, or Donnan potential, between thedilute and concentrated streams. Higher recovery may widen the Donnanpotential gap. Conversely, the early desalting stages can be operated athigher water recovery since the concentration difference is not as high.

The recovery rate of an ED can be described as:

$\Delta = \frac{Q_{prac}^{p}}{Q_{prac}^{f}}$

Here Δ is the recovery rate, Q_(prac) ^(p) the actual flow rate of theproduct and Q_(prac) ^(f) the actual total flow rate of the dilute andconcentrate streams. When ignoring the water migration due to osmosisand electroosmosis between the dilute and concentrate streams, therecovery rate can be calculated as:

$\Delta = \frac{Q^{dilute}}{Q^{dilute} + Q^{concen}}$

Here Q^(dilute) and Q^(concen) are the flow rates of dilute feed andconcentrated feed, respectively.

In conventional ED, a constant recovery rate is applied to the allstages of the entire desalting process. At the later stages of thisoperation, the concentrated stream becomes more concentrated and thedilute stream becomes more dilute. Thus a high concentration gradient isgenerated between the two streams, that is, a high Donnan potentialexists. The Donnan potential can be simply calculated as:

$\phi_{Don} = {\frac{RT}{z_{i}F}\ln \frac{C^{concen}}{C^{dilute}}}$

Here C^(concen) and C^(dilute) are the concentrations of the concentrateand dilute streams, respectively. The high Donnan potential means thatmore electric energy has to be applied to the ED system to overcome thehigh concentration gradient.

Typically, the dilute water from the first stage may be directed to thediluting compartments of the second stage and then to the third stageand beyond. If the concentrate water is also transferred from one stageto the other, the difference in concentration between the dilute andconcentrate compartment may increase which results in an increasingamount of voltage needed for ion removal from the dilute compartment tothe concentrate compartment. In order to counteract this effect, freshseawater may be introduced into the second stage or subsequent stageconcentrate compartments.

In an electrodesalination system with a plurality of stages, typicallyelectrodialysis modules are used towards the seawater inlet andelectrodeionization modules are used later in the process after thewater has been partially purified. The ion exchange resin contained inthe electrodeionization module helps to reduce the applied voltage whenthe water is low in conductivity. If an electrodeionization module isused on seawater, the impact of the ion exchange resin in the dilutecompartment is small. Conversely, if the water in an electrodialysismodule is too pure, a high electrical resistance will result whichcontributes to excess power consumption.

In accordance with one or more embodiments, the transition point betweenthe use of electrodialysis and electrodeionization may be strategicallydetermined and implemented. In accordance with one or more embodiments,the optimum transition point between ED and CEDI in the desalinationprocess may depend primarily on voltage drop. The factors contributingto the voltage drop in an ED/CEDI cell include the conductivity of thecell and the thickness of the cell. CEDI adds conductive media to thecell to increase the overall cell conductivity. There could be, however,limits to minimizing the thickness of a cell containing conductivemedia. In this case, the optimum transition point from ED to CEDIdepends heavily on the thickness of the two cells. For two giventhicknesses (with an ED cell typically thinner than a CEDI cell), theoptimum transition point will occur when the conductivity of thesolution decreases enough that the ED cell becomes less conductive thanthe thicker CEDI cell. In some non-limiting embodiments, the transitionpoint may be in a range of about 2000 to about 5000 mg/L. In someembodiments, the transition point may be in a range of about 2500 and3500 mg/L. In still other embodiments, the transition point may be in arange of about 2500 and 3000 mg/L. In some specific non-limitingembodiments, the transition point may be about 2800 ppm.

In accordance with one or more embodiments of electrodialysis orelectrodeionization modules, many cell pairs are bounded by a set ofelectrodes including an anode and cathode.

The cathode material may comprise 316L stainless steel, Hastelloy C, orother materials that are resistant to corrosion. The anode material cancomprise a base metal such as Titanium coated with a noble metal such asPlatinum or a rare earth oxide such as Iridium or Ruthenium Oxide orcombination thereof. A liquid may be used to flush the electrodecompartments in order to remove gases and chemicals that are generated.In some embodiments, the liquid used in the electrode compartments tominimize the voltage drop may be modified to reduce the powerconsumption. One method of reducing the voltage drop in the electrodecompartments is to use a liquid with a very high conductivity. Manyconcentrated salt solutions can be used such as sodium chloride orsodium sulfate. This liquid can comprise concentrated seawater forinstance. In another embodiment, strong acids and bases may be used toflush the electrode compartments. In some embodiments, if the cathodecompartment is flushed with a hydrochloric acid solution of between a pHof 0.5 to 2, the voltage drop may be minimized compared to the use ofother liquids. In at least some embodiments, the anode compartment maybe flushed with either concentrated seawater or sodium hydroxide orhydrochloric acid.

The concentration difference between the dilute and concentrated streams(Donnan potential) increases during desalination, and the energyrequired to overcome the concentration difference also increases as aresult. In accordance with one or more embodiments, a multiple dumpingstrategy for the concentration stream may reduce the energy forovercoming the Donnan potential.

In accordance with one or more embodiments, electrode solutions may bevaried. Voltage loss in the electrode compartment is dependant on thetype of electrolyte used. An ideal electrolyte should have low voltageloss and minimizes risk of scaling.

With respect to the cathode compartment, hydroxyl ions are generatedduring the reduction process. Scaling is a concern in the choice ofcatholyte. Hydrochloric acid is the preferred choice for catholytebecause it has low voltage loss and it minimizes scaling risk. In someembodiments, low catholyte pH can be achieved via a feed-and-bleed modein which the catholyte stream is connected in a re-circulating loop toan acid feed tank. The acid tank is controlled, for example, at pH 3.Hydrochloric acid may be dosed into the acid tank to maintain the pHlevel. The acid tank may be drained occasionally to prevent hardnessions saturation. In other embodiments, low catholyte pH can be achievedvia direct injection of hydrochloric acid into the catholyte streamusing raw seawater as a catholyte feed solution. The pH of the catholytestream may be maintained, for example, at pH 3. This mode may allowoperation without a bulky acid feed tank.

H₂O+e→½H₂+OH⁻

With respect to the anode compartment, proton ions are generated duringthe oxidation process. Sodium hydroxide or hydrochloric acid as anolytemay result in the lowest voltage loss.

However, for cost and safety reasons, raw seawater may be used in theanode compartment. The module reject stream (concentrated stream) canalso be used without any operational issues. This will result in minorsavings of pre-treated raw sea water.

Cl⁻−e→½Cl₂

In accordance with one or more embodiments, ED stage-1 product water maybe used as both catholyte and anolyte. Because most of the hardness willbe removed early during the ED desalting process, the product water fromstage-1 will contain low hardness. This stream can be first directed tothe anode compartment, which will produce an acidic anode outlet.Subsequently, the product of the anode may be directed to the cathodecompartment. HCl acid may be injected to maintain the pH of the cathodestream at a level less than 3. This may reduce the acid consumption forthe cathode compartment. FIG. 12 presents an example of the ratio ofremaining sodium, calcium and magnesium as a function of conductivity.

In other embodiments, the electrochemical deionization device cancomprise a capacitive deionization device. This device uses a pluralityof electrodes situated in parallel. A voltage of, for example,approximately 1.2 may be applied to the electrodes while water is passedbetween the electrodes. Ionic material is attracted to the electrodesurface resulting in an effluent with reduced ionic content. Once theelectrode pores or surface is saturated with ions, the polarity of theelectrodes is reversed and the water diverted to drain. This is a batchtype process as opposed to a continuous process. Capacitive deionizationcan be used either in conjunction with other types of electrochemicaldeionization devices or alone in an electrodesalination system.

In accordance with one or more embodiments, pretreatment, disinfectionand/or cleaning in place (CIP) may be implemented in desalinationprocesses. In some embodiments, sodium hypochlorite may be used asdisinfectant. A potential dosing point is at the ED feed tank. In somenon-limiting embodiments, the estimated contact time may be more than 10sec before feed to ED module. The tank chlorine residual may be set, forexample, as 0.5 ppm, or ORP reading over 650 mV.

In some embodiments, when raw seawater, ED stage-1 product or EDconcentrate is used as the electrode stream, the anode reaction maygenerate chlorine gas. The anode stream outlet (with the chlorine gas)may be channeled to the feed tank as a source of disinfectant. Strategicuse of analyte may eliminate the need for sodium hypochlorite in wholeor in part.

In accordance with one or more embodiments, CIP may be implemented tocontrol bacteria fouling. In one procedure, sodium hypochlorite andhydrochloric acid may be added to raw seawater. A cleaning solution maybe prepared with residual free chlorine at 20 ppm. The pH level of thecleaning solution may be maintained at about 6 with the addition ofhydrochloric acid. This may prevent the cleaning solution from becomingalkaline after addition of sodium hypochlorite. An alkaline cleaningsolution will result in lower chlorine disinfection efficacy andprecipitation of metals. The cleaning solution may be recirculated at avelocity of about 2 cm/s for a duration of about 20 mins. The ED devicemay then be flushed with seawater for about 10 mins before the ED deviceis returned to service.

In accordance with one or more embodiments, CIP may be implemented tocontrol hardness scaling. In one example procedure, hydrochloric acidmay be added to raw seawater. A cleaning solution may be prepared withthe addition of hydrochloric acid to a pH set-point of about 2. Acid maybe injected when required to maintain the pH level. The cleaningsolution may be recirculated at a velocity of about 2 cm/s for aduration of about 20 mins. The ED device may then be flushed withseawater until the outlet pH level is greater than about 6 before the EDdevice is returned to service.

In accordance with one or more non-limiting embodiments, an overalltreatment process may include disk filter treatment followed byultrafiltration, followed by electrochemical desalination, followed bypost-treatment operations.

Purified water may be sent for use or storage as potable water. Potablewater may be preserved or further disinfected, if desired, and may finduse in various applications including agriculture and industry, such asfor semiconductor fabrication. A reject or concentrate stream producedby the electrochemical device may be collected and discharged to waste,recycled through the system, or fed to a downstream unit operation forfurther treatment. Product streams may be further processed prior todownstream use, upstream use, or disposal. For example, a pH level of aproduct acid or product base stream may be adjusted. In someembodiments, it may be desirable to mix, in part or in whole, one ormore product streams. One or more additional unit operations may befluidly connected downstream of the electrochemical unit. For example,one or more unit operations may be configured to receive and process atarget product stream, such as before delivering it to a point of use.Polishing units, such as those involving chemical or biologicaltreatment, may also be present to treat a product or effluent stream ofthe device prior to use or discharge.

In accordance with one or more embodiments, one or more sensors may bepositioned to detect one or more characteristics, conditions, propertiesor states of any stream, component or subsystem generally associatedwith the device. In some non-limiting embodiments, one or more of thesensors may be configured to detect a concentration of a target speciesin a stream entering or exiting the device. In one embodiment, one ormore sensors may be positioned to detect a concentration at an inletand/or an outlet of one or more compartments of the device. In anothernon-limiting embodiment, one or more sensors may be positioned to detecta pH level at an inlet and/or an outlet of one or more compartments ofthe device. In still other embodiments, a pressure sensor may beassociated with one or more compartments of the device. In yet otherembodiments, sensors for detecting TDS may be implemented.

In some embodiments, devices and methods involve a controller foradjusting or regulating at least one operating parameter of the deviceor a component of the system, such as, but not limited to, actuatingvalves and pumps, as well as adjusting a property or characteristic of acurrent or an applied electric field through the electrically drivenseparation device. The controller may be in electronic communicationwith at least one sensor configured to detect at least one operationalparameter of the system. The controller may be generally configured togenerate a control signal to adjust one or more operational parametersin response to a signal generated by a sensor. For example, thecontroller can be configured to receive a representation of a condition,property, or state of any stream, component or subsystem of the device,or from the device. The controller typically includes an algorithm thatfacilitates generation of at least one output signal which is typicallybased on one or more of any of the representation and a target ordesired value such as a set point. In accordance with one or moreparticular aspects of the invention, the controller can be configured toreceive a representation of any of a measured property of any streamfrom the device, and generate a control, drive or output signal to anyof the treatment system components, including the device, to reduce anydeviation of the measured property from a target value.

In accordance with one or more embodiments, a controller may beconfigured to reverse polarity of an electric current applied throughthe device. The controller may be in communication with one or moresensors configured to provide a measurement signal which isrepresentative of a concentration of a target species in a streamassociated with the device, for example, a product stream exiting acompartment of the device. In some embodiments, a conductivity level,pressure or concentration measurement may be detected by a sensor andcommunicated to the controller. The controller may be configured togenerate a control signal in response a received measurement being aboveor exceeding a predetermined level. The control signal may reversepolarity of an electric current applied through the device so as toregenerate a membrane or media in a compartment therein. In someembodiments, the control signal may be sent to a power supply associatedwith the device based at least partially on the measurement signal.

In other configurations, the controller can be in open-loop control,providing or changing one or more operating conditions of at least onecomponent of the treatment system. For example, the controller canperiodically generate output or drive signals, typically according to apredefined schedule, that reverses the polarity of the applied electricfield, and preferably, the stream flow paths through the device, from apredetermined arrangement to a second predetermined arrangement.

One or more sensors implementable in the systems and methods can providea representation of a property or characteristic of a stream into, from,or within the device, or a property or characteristic of a currentapplied through the device. For example, the one or more sensors can beconfigured to measure and provide a representation, e.g., a measuredsignal, of a process condition such as the pH of any stream exiting anyof the compartments. The one or more sensors can also provide measuredconductivity or resistivity values of any of the streams into, from orwithin the device. In particularly advantageous configurations, at leastone sensor can be utilized to provide a representation, by directmeasurement or by proxy, of the concentration of at least one targetspecies in the product stream from the device, or from any of thecompartments. Measurement of concentration can be effected by, forexample, techniques wherein samples are batch-wise periodicallyretrieved and analyzed, or analyzed semi-continually through one or moreside streams.

Prior to treatment of feed water in the electrochemical device, avariety of pretreatment procedures can be employed. For example,pretreatment techniques may be utilized on a feed water that may containsolids or other materials that may interfere with or reduce theefficiency of any stage or device, such as by scaling or fouling. Anoptional initial treatment may be provided to remove at least a portionof suspended solids, colloidal substances and/or solutes of elevatedmolecular weight. Pretreatment processes may be performed upstream ofthe EDI device and may include, for example, particulate filtration,sand filtration, carbon filtration, ultrafiltration, nanofiltration,microfiltration, such as cross-flow microfiltration, combinationsthereof and other separation methods directed to the reduction ofparticulates. Adjustments to the pH and/or alkalinity of feed water mayalso be performed by, for example, the addition of an acid, base orbuffer, or through aeration. Electrochemical separation may follow anypretreatment operation to provide water having a desired final purity.

The electrochemical devices may be operated in any suitable fashion thatachieves the desired product and/or effects the desired treatment. Forexample, the various embodiments can be operated continuously, oressentially continuously or continually, intermittently, periodically,or even upon demand. Multi-pass systems may also be employed whereinfeed is typically passed through the device two or more times, or may bepassed through an optional second device. An electrical separationdevice may be operatively associated with one or more other units,assemblies, and/or components. Ancillary components and/or subsystemsmay include pipes, pumps, tanks, sensors, control systems, as well aspower supply and distribution subsystems that cooperatively allowoperation of the system.

It should be understood that the systems, techniques and methods may beused in connection with a wide variety of systems where the processingof one or more liquids may be desired. Thus, the electrical separationdevice may be modified by those of ordinary skill in the art as neededfor a particular process, without departing from the scope of theinvention.

The function and advantages of these and other embodiments will be morefully understood from the following non-limiting example. The example isintended to be illustrative in nature and is not to be considered aslimiting the scope of the embodiments discussed herein.

Prophetic Example

Seawater has a concentration of about 35,000 mg/l of total dissolvedsolids (TDS) or a conductivity of about 46 mS/cm. If the set point ofthe first stage is 25 mS/cm and the water recovery is about 50%,(calculated by the equation; % recovery=(dilute flow/diluteflow+concentrate flow)×100) the conductivity of the concentrate from thefirst stage will be about 67 mS/cm. If the water from the first stagedilute and concentrate is used to feed the dilute and concentratestreams respectively on the second stage, the Donnan voltage will beabout 25.31 mV/cell pair. If, however, fresh seawater is used to feedthe concentrate stream in the second stage, the Donnan voltage will beabout 15.66 mV/cell pair, a 40% reduction. This is just one example ofhow varying the recovery and conductivity of the water used to feed theconcentrate stream can affect the overall power consumption of theelectrodesalination process. Many different combinations of feedingseawater to subsequent stage concentrate streams can be used to obtainthe lowest possible Donnan voltage between the dilute and concentratestreams. Co-flow and counter-flow configurations and combinations arealso possible.

Example 1

Experiments were conducted to determine where the transition point withrespect to power consumption versus salt removal should be between theuse of electrodialysis and electrodeionization. The transition point wasdetermined to be between 2600 mg/l to about 5000 mg/l with the preferredtransition point in the range of 3000 mg/l to 3500 mg/l. By using anelectrodeionization module in the process train when the water ispurified to this range, the power consumption of the process wasminimized.

Example 2

A four stage electrodesalination system comprising three stages ofelectrodialysis and one stage of electrodeionization was tested onnatural seawater. The pretreatment consisted of sand or mediafiltration, chlorination, and cartridge depth filtration. The processdiagram for the electrodesalination system is shown in FIG. 5. The EDdilute was provided in series flow and the ED concentrate was providedin parallel flow. Stages 1-3 each included an ED module. Stage 4included three parallel EDI modules. Fresh seawater was used asconcentrate feed for the concentrate for each stage. A PID control wasused to control the voltage and current to each module independently bysensing the inlet and outlet conductivity of the dilute stream. Theelectrodialysis modules used for the first two stages utilized a threepass folded path configuration. The third electrodialysis stage used afive pass folded configuration. The electrodeionization module used atwo pass folded path configuration. The inlet conductivity averagedabout 46 mS/cm. The outlet conductivity was approximately 1 mS/cm orabout 500 mg/l of TDS. The system operated for 1600 hours with anaverage power consumption of 1.8 kwh/m3 as shown in FIG. 6A illustratingpower consumption as a function of time. The power consumption reflectedthe total of desalination power, pumping power, electrode losses andother inefficiencies. Conductivity data is presented in FIG. 6B. Theaverage seawater conductivity was about 32,000 ppm TDS and the averageproduct water conductivity was about 500 ppm TDS. Module resistance datais shown in FIG. 6C. Resistance was generally stable with fluctuationsdue to variation in product water quality and current setpoint. CEDIresistance was likely lower due to resins in dilute compartments.Flowrate data is presented in FIG. 6D. System flowrate was allowed tofluctuate, thus keeping the pressure drop constant. The total systempressure drop was about 1.5 bar. The overall recovery rate was about30%. The performance of the electrodesalination process in terms ofpower consumption is substantially improved compared to otherdesalination technologies.

Example 3

Laboratory experiments indicated that about 5% energy savings ispossible using variable water recovery in accordance with one or moreembodiments.

A high recovery rate was applied during the initial phase of thedesalting process and a low recovery rate was applied at the laterstages. The goal was to maintain the lowest possible ratio of the streamconcentrations between the concentrate and dilute compartments. This isbeneficial to reducing the energy penalty caused by the Donnan effect.

As shown in the laboratory experimental data, one method is to dump theconcentrate stream at every 4th stage in the whole 21 stages. The otherway is to dump the concentrate stream at 6th, 11 th, 15th, 18th, 20thstages. For these two operations, the entire water recovery rate is thesame. From the experiments, the second method benefits to keep amoderate concentration gradient between the streams (ratio 8.2 comparedto 11.4 in the first method). This variable recovery rate operation cansave about 5% energy in the desalting process. FIG. 3 illustrates theED/CEDI transition point with variable recovery and data of energyconsumption vs. ppm TDS in ED product. FIG. 4 illustrates variablerecovery with fresh seawater and data of voltage drop per cell pairversus product TDS.

Example 4

An ED configuration was demonstrated with seawater using a velocityprofile. FIG. 7 illustrates the old and new configurations. In the newconfiguration, an increased velocity was applied in Stage 2. Table 3indicates the velocity profile of ED Stages 1 and 2 afterreconfiguration.

TABLE 3 Cell pairs per Nominal velocity Pass pass (cm/sec) ED-1 1 1820.48 2 164 0.53 3 148 0.59 4 130 0.67 5 120 0.73 ED-2 1 170 0.48 2 1500.54 3 140 0.58 4 120 0.67 5 80 1.01 6 60 1.35

FIG. 8 illustrates improvement in process efficiency after increasingvelocity in Stage 2. FIG. 9 illustrates a decrease in Stage 2 moduleresistance after increasing velocity in Stag 2. FIG. 10 illustrates adecrease in overall power consumption after increasing velocity in Stage2.

Example 5

Multiple dumps on the concentrated stream was demonstrated. Indesalination ED modules, the concentrated stream consisted of two dumpsfor each module, both parallel to the fresh seawater inlet.

The desalination energy consumption with different concentrated streamdumping was calculated as shown in Table 4 with the followingassumptions: (1) desalinating 35000 ppm NaCl, 25° C., to product 500ppm, (2) membrane area resistance 2.8 ohm-cm2, and current density 35A/m2, (3) alpha parameter (reflecting compartment volume occupied byscreen) 0.45, and beta parameter (reflecting membrane surface areaoccupied by screen) 0.70, (4) osmotic permeability 4.5 ml/(m2·hr·bar),and electroosmotic permeability 3.7 mol-Water per Faraday, (5) waterrecovery 40%, (6) ignoring current efficiency loss, (7) ignoringelectrode voltage.

TABLE 4 Energy Dumping number (kWh/m3) 1 2.2621 2 1.8332 4 1.6865 101.6203

FIG. 11 illustrates the spacer configuration and method of multipleconcentrate dumps/passes in an ED module.

Example 6

Experiments were conducted to establish the transition point for a givenspacer thicknesses. Thicknesses were chosen to match the likelythicknesses to be used in a demonstration desalination plant. Theexperiments consisted of desalinating NaCl and synthetic seawatersolutions with an ED module and a CEDI module. Voltage drop data wascollected during each run and plotted for comparison. FIGS. 13 and 14display the results. FIG. 13 presents ED. vs. EDI for NaCl desalination.FIG. 14 presents ED vs. CEDI for synthetic seawater desalination. ForNaCl solutions, the optimum transition point for these thicknesses wasshown to be about 2800 ppm TDS. For synthetic seawater solutions, theoptimum transition point for these thicknesses was shown to be about3000 ppm.

This transition point is subject to change with differing thicknessesand solution conductivities. For example, when testing with thinner EDspacers of 0.38 mm thickness, the optimum transition point moved toabout 2600 ppm and this trend would likely continue as the thickness gapbetween ED and CEDI decreases. Also, depending on the ionic makeup of agiven solution, the conductivity may be different for a given TDS. Forexample, seawater is less conductive than a NaCl solution for a givenTDS. This likely explains the difference in transition point in theexperiments.

Example 7

A four stage system as schematically presented in FIG. 15 was operatedat the indicated velocities. Each module contained 2880 cell pairs. A40% recovery at 2.0 kWh/m³ was achieved. It was demonstrated thatreduced flow rate yielded greater energy efficiency.

While exemplary embodiments of the disclosure have been disclosed manymodifications, additions, and deletions may be made therein withoutdeparting from the spirit and scope of the disclosure and itsequivalents, as set forth in the following claims.

Those skilled in the art would readily appreciate that the variousparameters and configurations described herein are meant to be exemplaryand that actual parameters and configurations will depend upon thespecific application for which the electrical purification apparatus andmethods of the present disclosure are used. Those skilled in the artwill recognize, or be able to ascertain using no more than routineexperimentation, many equivalents to the specific embodiments describedherein. For example, those skilled in the art may recognize that theapparatus, and components thereof, according to the present disclosuremay further comprise a network of systems or be a component of a waterpurification or treatment system. It is, therefore, to be understoodthat the foregoing embodiments are presented by way of example only andthat, within the scope of the appended claims and equivalents thereto,the disclosed electrical purification apparatus and methods may bepracticed otherwise than as specifically described. The presentapparatus and methods are directed to each individual feature or methoddescribed herein. In addition, any combination of two or more suchfeatures, apparatus or methods, if such features, apparatus or methodsare not mutually inconsistent, is included within the scope of thepresent disclosure.

For example, the housing may be of any suitable geometry such that oneor more membrane cell stacks or modular units may be secured within. Forexample, the housing may be cylindrical, polygonal, square, orrectangular. With regard to the membrane cell stacks and modular units,any suitable geometry is acceptable so long as the cell stack or modularunit may be secured to the housing. For example the membranes or spacersmay be rectangular in shape. In certain embodiments, a housing may notbe required. The geometry of the membranes and spacers may be of anysuitable geometry such that the membranes and spacers may be securedwithin a cell stack. In certain embodiments, the geometry of any of thehousing, cell stack, membranes, and spacers may selected to accommodateoperational parameters of the electrical purification apparatus. Forexample, the spacers may be asymmetrical to accommodate differences inflow rates between the dilute and concentrate streams.

Further, it is to be appreciated various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe disclosure. For example, an existing facility may be modified toutilize or incorporate any one or more aspects of the disclosure. Thus,in some cases, the apparatus and methods may involve connecting orconfiguring an existing facility to comprise an electrical purificationapparatus. Accordingly, the foregoing description and drawings are byway of example only. Further, the depictions in the drawings do notlimit the disclosures to the particularly illustrated representations.

As used herein, the term “plurality” refers to two or more items orcomponents. The terms “comprising,” “including,” “carrying,” “having,”“containing,” and “involving,” whether in the written description or theclaims and the like, are open-ended terms, i.e., to mean “including butnot limited to.” Thus, the use of such terms is meant to encompass theitems listed thereafter, and equivalents thereof, as well as additionalitems. Only the transitional phrases “consisting of” and “consistingessentially of,” are closed or semi-closed transitional phrases,respectively, with respect to the claims. Use of ordinal terms such as“first,” “second,” “third,” and the like in the claims to modify a claimelement does not by itself connote any priority, precedence, or order ofone claim element over another or the temporal order in which acts of amethod are performed, but are used merely as labels to distinguish oneclaim element having a certain name from another element having a samename (but for use of the ordinal term) to distinguish the claimelements.

What is claimed is:
 1. A desalination system, comprising: anelectrodialysis (ED) device; an electrodeionization (EDI) device fluidlyconnected downstream of the ED device; and a controller configured todetermine an optimum transition point between the ED and EDI deviceswith respect to power consumption and salt removal, and furtherconfigured to bring the EDI device online when a product stream of theED device achieves the optimum transition point.
 2. The system of claim1, wherein the optimum transition point is based on voltage drop.
 3. Thesystem of claim 1, wherein the optimum transition point is based on cellthickness.
 4. The system of claim 1, wherein the optimum transitionpoint is based on conductivity.
 5. The system of claim 1, wherein theoptimum transition point is between about 2500 ppm and about 3000 ppm.6. The system of claim 5, wherein the optimum transition point is about2800 ppm.
 7. The system of claim 1, wherein the controller is furtherconfigured to adjust a pH level of an electrolyte in at least one of theED and EDI devices.
 8. The system of claim 1, further comprising apretreatment unit fluidly connected upstream of the ED device.
 9. Thesystem of claim 1, wherein the controller is further configured toperform a disinfecting or cleaning-in-place operation on at least one ofthe ED and EDI devices.
 10. A method of providing potable water,comprising: fluidly connecting a seawater feed stream to an inlet of anelectrical purification system, the system comprising at least a firststage and a second stage downstream of the first stage; recovering waterfrom the first stage at a first rate; recovering water from the secondstage at a second rate that is less than the first rate; and fluidlyconnecting an outlet of the electrical purification system to a potablepoint of use.
 11. The method of claim 10, further comprising maintaininga target concentration gradient between concentrate and dilutecompartments in each of the first and second stages.
 12. The method ofclaim 11, further comprising performing multiple dumps of a concentratestream associated with at least one stage of the electrical purificationsystem.
 13. The method of claim 10, further comprising adjusting a pHlevel of an electrolyte in the electrical purification system.
 14. Themethod of claim 10, further comprising performing a disinfecting orcleaning-in-place operation on the electrical purification system. 15.The method of claim 10, wherein the electrical purification systemcomprises a capacitive deionization device.
 16. A method of providingpotable water, comprising: fluidly connecting a seawater feed stream toan inlet of an electrical purification system, the system comprising atleast a first electrodialysis (ED) stage and a second ED stagedownstream of the first ED stage; inhibiting concentration polarizationby passing a process stream through a dilute compartment in the secondED stage at an increased velocity relative to the first ED stage; anddelivering potable water to a point of use downstream of the electricalpurification system.
 17. The method of claim 16, wherein the first EDstage includes at least a first pass and a second pass, and wherein thefirst pass has a different number of cell pairs than the second pass.18. The method of claim 16, wherein the second ED stage includes atleast one blocking spacer.
 19. A desalination system, comprising: anelectrical purification system comprising at least a firstelectrodialysis (ED) stage and a second ED stage fluidly connecteddownstream of the first ED stage; at least one conductivity sensorassociated with the electrical purification system; and a controllerconfigured to apply a first voltage to the first ED stage and to apply asecond voltage, lower than the first voltage, to the second ED stagebased on input from the conductivity sensor to inhibit concentrationpolarization.
 20. The system of claim 19, wherein the controller isfurther configured to adjust the voltage applied to the first ED stageto achieve a target conductivity at an outlet of the first ED stage.